Doors are known devices which are used to control access to buildings such as garages, warehouses and barns. Doors can be in a closed position, thus preventing access to the building. Doors can also be moved to an open position, thus allowing access to the building.
Known prior art doors include single panel doors. One example is a hydraulic door 10 having a single panel 12, as shown in FIG. 1. In the closed position, the single panel 12 lies vertically in the plane of the door opening 14. To open the door 10, hydraulic cylinders 16 are used to raise the entire single panel 12 away from the door opening 14 until the panel 12 is almost or completely perpendicular to the plane of the door opening 14, as shown in FIG. 1. To open such a door 10, this single panel 12 needs to swing in a very large arc or radius which can interfere with objects outside the building such as parked cars. Furthermore, when in the open position, the single panel 10 is supported at only one end 18 and forms a cantilvered mass. The single panel 12 will be subject to torque about end 18 in the counterclockwise direction. Therefore, the panel 12 will tend to swing back into the closed position. The torque will increase as the mass of the panel 12 increases. Doors for larger buildings, such as warehouses and barns, are often very heavy, generally weighing ½ ton to 1 ton or more. Therefore, extensive support structure is often required to maintain this single panel 12 in the open cantilevered position. The installation of the necessary support structure, especially for older buildings, requires extensive and costly renovation. For example, the door frame defining the door opening may be made of material that is not strong enough to support a cantilevered door, and therefore, would need to be replaced with a door frame made of stronger material.
Other known doors include single panel doors, where the single panel moves into the interior of the building when in an open position. Specifically, the single panel moves into and is supported by an overhead guide rail which is fitted into the interior of the building. The installation of such overhead guide rails is costly, and the overhead guide rails waste vertical space in the building.
Known doors also include bi-fold doors 50, as shown in FIG. 2. These doors 50 have an upper panel 52 and a lower panel 54 which are pivotally connected to each other by a hinge 56. When in a closed position, the upper panel 52 and the lower panel 54 of the bi-fold door 50 lie vertically in the plane of the door opening 58, with the upper panel 52 directly above the lower panel 54. To open the door 50, the upper panel 52 and the lower panel 54 pivot towards each other about the hinge 56 until the upper panel 52 is disposed in a position almost flat on top of the lower panel 54. When in an open position, the upper panel 52 lies almost flat on top of the lower panel 54. There is a cantilevered mass because the upper panel 52 and the lower panel 54 are only supported at one end 60. There is a tendency for the upper panel 52 and the lower panel 54 to unfold or sag back into the closed position. The upper panel 52 is subject to torque about end 60 in the clockwise direction, and therefore, will push downwards on the lower panel 52 which leads to unfolding or sagging. A significant amount of structural support is often required to keep such bi-fold doors in the open position. As mentioned above, doors often weigh ½ ton to 1 ton or more.